Which of these numbers is composite? ${7,\ 13,\ 23,\ 77,\ 79}$
Answer: A composite number is a number that has more than two factors (including 1 and itself). 7, 13, 23, and 79 each have only two factors. The factors of 77 are 1, 7, 11, and 77. Thus, 77 is the composite number.